List<String> empty, but values return after reload

Question

I'm trying to load different values from a .txt file line by line.

I'm loading an file from assets, which is already registered in pubspec.yaml.

Future<String> getFileData() async {
  return await rootBundle.loadString('assets/files/text.txt');
}

As this returns one long String I split it into a list:

void doStuff() async {
  await getFileData().then((value) => value.split('\n').forEach((element) {
        exampleQuestions.add(element);
      }));
}

This method is called in my class - constructor which is called from my Main by a named route:

  GameOver.routeName: (context) => GameOver(),
    '/game': (context) => Game(

        ),
  },

exampleQuestion get's filled in the doStuff() - method (already checked that), but looses it's values in the _GameState class where the widget, that want's to access the list returns an out of index exception.

However if i quick reload my application the values are set correctly. If I then click the button to continue again nothing changes until I quick reload.

Any hints are very appreciated ..

try to use setState method when you add elements to the list — Sal Man
– Sal Man, Commented Apr 26, 2021 at 0:43

hacker1024 · Accepted Answer · 2021-04-26 03:15:36Z

1

You should not call asynchronous methods like this in widget constructors, because they'll be called on every build.

You should use a StatefulWidget with a FutureBuilder instead.

On another note, LineSplitter should be used for splitting lines.

class _MyWidgetState extends State<MyWidget> {
  late final Future<List<String>> _exampleQuestionsFuture;

  static Future<String> _getFileData() => rootBundle.loadString('assets/files/text.txt');

  @override
  void initState() {
    super.initState();
    _exampleQuestionsFuture = _getFileData().then(const LineSplitter().convert);
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<List<String>>(
      future: _exampleQuestionsFuture,
      builder: (snapshot, data) {
        /* ... */
      },
    );
  }
}

answered Apr 26, 2021 at 3:15

hacker1024

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5 Comments

Danzon2504 Over a year ago

Thanks for the answer. How can I read from the Future<List<String>> now ? I tried something like: @override void initState(){ super.initState(); _getFileData().then(const LineSplitter().convert).then((value) { setState(() { question = value.elementAt(currentRound); }); }); but from my understainding this makes no sense, because the value is only updated once.

Danzon2504 Over a year ago

question: _exampleQuestionsFuture.then((value) => value.elementAt(currentRound)) , returns with cannot applie Future<String> to String

hacker1024 Over a year ago

Use the snapshot in FutureBuilder. FutureBuilder is made for single-use Futures.

hacker1024 Over a year ago

Great! Be sure to mark this answer as accepted if it worked for you.

Danzon2504 Over a year ago

How can i get the length of the _exampleQuestionsFuture now? I tried different approches, but always run into the problem , that at some point i cannot convert Future<int> to int

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